Electrical surge diverting connector

ABSTRACT

An electrical connector which provides lightning protection by facilitating arcing of electrical surges over the end of an insulator and cooperating conductive surface employing dielectric to stimulate arc-over and thus substantially reduce breakdown voltage.

United. States Patent Cooper t 1 Nov. 7, 1972 [s41 ELECTRICAL SURGE DIVERTIN [56] References Cited 0 CONNECT R lb UNITED STATES PATENTS [72] l 3; Cmpe" A uquerque 2,906,925 9/1959 Yonkers et a1. 317/61 2,965,779 12/1960 Zalesak ..3l3/51' [73] Assignee: The UnitedStates of America as, ]3,45 0,923 6/1969 Brumm ..3l7/62X represented by the United States Atomi En rgy Commi ion j" 'irimary Examiner-James D. Trammell 221 Filed: Dec. 21, 1971 147"? Roland Anderson [21] Appl. No.: 210,370 I ABSTRACT v 1 An electrical connector which provides lightning pro- {521 U S Cl 317/61 313/51 317/62 tection by facilitating arcingof electrical surges over [5]] 6 0 the end of an insulator and cooperating conductive surfacegemploying dielectric to stimulate arc over and [58] Field of Search ..339/111; 317/61, 61.5,62;

thus substantially reduce breakdown voltage.

11 Clairns, s nrawin Figures VPTATEN'T'EDIIHVI 71912 7 r 3.702420 O I 0.5- |.O L5 2.0 IMPULSE-RATIO BEHAVIOR (IO-MIL DIELECTRIC-STIMULATED ARC GAP) I9 INVENTOR. JAMES A. COOPER ELECTRICAL SURGE DIV RTING CONNECTOR BACKGROUND or INVENTION Lightning canbe a serious hazard to missiles and aircraft. Possible adverse effects include structural damage, fuel detonation, component burnout or malfunction, and ignition of explosives. An unlikely but objectionable. effect would be the accidental detonation of on-board explosives.

Not only is a lightning strike upon a missile or aircraft possible, but such a strike can be triggered by the vehicles entry into a properly charged region. This triggering can take place even in areas where there is no apparent lightning activity. Since missiles and aircraftcannot always be operated in ideal weather, the potential lightning hazard must be considered in detail, especially with regard to safety;

Characterization of the lightning threat is difficult because its intensity and theunpredictability of strike locations and time make measurements difficult. However, a considerable amount of data is available. A typical lightning strike comprises multiple pulses of high current superimposed on a relatively small continuing or follow-on current. Pulses are distinguished by relatively steep leading edges and more slowly and decaying trailing edges. Currentcan flow in either direction, but negative charge is lowered to ground in most strikes. Further, it has been demonstrated that lightning characteristics in striking a tall building are different than the characteristics of lightning striking an open field, a missile or an aircraft in flight.

From a study of the data-available, it may be concluded that there is an averageof three pulses per stroke with a maximum value of more than thirty; peak currents average about 20,000 amperes (kA) with maximum values of over 200 kA; rise times average about 2.5 micro (i4) seconds (sec) with minimum times as short as 0.3 14 sec; follow-on current averages about 250 amperes (A) with maximum values over 1 kA; and total strike duration averages about 0.2 seconds with maximum values greater than 1 second. I

In order to provide lightning protection against the lightning characteristics such as outlined above, various approaches have been tried; varistor stacks, air

- gaps, gas tubes, zener devices, fuses, lightning rods, filters, energy activated switches, etc. However, there has not been provided essentially 100 percent reliability against strokes in excess of 200,000 amperes and within electrical connector size constraints.

SUMMARY OF INVENTION In view of the limitations and problems as noted above, it is an object of this invention to provide a novel electrical surge diverting connector which overcomes prior art limitations.

It is an object of this invention to provide a lightning arrestor electrical connector suitable for use on aircraft, missiles, weapons, etc.

It is an object of this invention to provide a current and voltage overload switching electrical connector that is structurally simple, mechanically well sup- Various other objects and advantages will appear and be understood from the following description of the invention and are particularly pointed out hereinafter in connection with the appended claims. Various changes in design, details, materials, etc., as described herein may be made by those skilled in the art without departing from the scope and principles of the invention as brought out in the appended claims. It should be noted that the description of this invention is not intended to restrict or limit the use of this device to lightning arrestors but may be used wherever compact, current or voltage overload switching means are required.

The invention comprises a current or voltage overload switching electrical connector which makes use of dielectrics to facilitate or stimulate an are at a reduced voltage, which feature permits excellent equipment protection and compact electrical connector structure.

DESCRIPTION OF DRAWING FIG. 1 is a cross-sectional side view of one embodiment of this invention;

' FIG. 2 is an end view of another arrangement of this invention; 7

FIG. 3 is a cross-sectional, fragmentary view of another embodiment of this invention;

7 FIG. 4 is a graph plotted for linear ramp waveforms with varying rise time which represents values for the breakdown voltage vs time aspect with rutile, porcelain and air as parameters; and

FIG. 5 is a fragmentary, cross-sectional view of a modified form of this invention.

DETAILED DESCRIPTION FIG. 1 is illustrative of one embodiment of electrical surge diverting electrical connector 10 which incorporates features of this invention. Electrical connector 10 may include an electrically conductive, generally tubular housing 1 l which may have a plurality of ports 31 therethrough which may be at circumferentially spaced locations, and also having flange or other supporting means 12 for mounting said electrical connector 10 on a body or member 35 having apparatus or materials therein or associated therewith which are desired to be protected. Flange means 12 may also be used to conduct and dissipate the electrical energy received from a lightning strike to the body 35 on which flange means 12 may be mounted through suitable attaching and other conductive interconnecting means 13. Generally tubular housing 11 may also include opposing, partially bored or otherwise hollowed out passageways 14 and 15 which may be called the output end passageway 14 and input end passageway 15. While FIG. 1 shows ports 31 located on the input end 15 above flange means 12, thefla'nge 12 could be located at any suitable location even being beyond the ports 31 on the input end 15 side. An apertured first wall portion 25 may be located ported, and has very good transient impulse-ratio;

responses.

handling capability. 1

extending transversely of housing 11 adjacent ports 31 and a' second apertured wall portion 18 may extend transversely of housing 11 adjacent ports 31 at a location spaced from first wall portion 25 so as to form with first wall portion 25 an intermediate discharge chamber 27 in communication with ports 31 and second wall portion 18. Second wall portion 18 may have an exposed electrically conductive surface 34 disposed toward discharge chamber 27 and electrically commu- 1 nicating with electrically conductive housing 1 1.

An appropriate number and arrangement of electrical conductors or conductor pins 19 extend through the apertures of the first and second wall portions 25, 18 and have exposed electrically conductive areas 19a adjacent electrically conductive surface 34. FIG. 2 shows one elevation or end view of an embodiment containing 17 conductors which may be used. More or less conductors in-the same or different arrangements may be successfully used.

Electrically insulating sleeve means 20 encircle the conductors 19 and maintain the conductors 19 in spaced relationship with the second wall portion 18 and from electrically conductive surface 34. Sleeve portions ends 21 terminate at locations substantially devoid of projection beyond electrically conductive surface 34 into discharge chamber 27. Electrical surges may therefore divert from conductors 19, across the sleeve end 21, to electrically conductive surface 34 and on to housing 1 1.

Sleeve means 20 may be of any appropriate material such as rutile, alumina, barium titanate and the like. Dielectric material having a dielectric constant greater than about 4 and preferably greater than about 50 gives good results. Dielectric constants referred to herein have been measured at frequencies below about cycles per second and are generally constant in this region at room temperature of about 25 C. The surface 21 of this high dielectric constant electrically insulating sleeve means 20 is adapted to assist in initiating an arcover to the second wall portion 18, i.e., the dielectric sleeve means 20 facilitates or'stimulates an are from a conductor 19 to the second wall portion 18, and on to the exterior or walls of the body 35 containing apparatus and equipment sought to be protected, using a dielectric simulated arc (DSA).

A suitable potting material 30, such as certain silicones like room temperature vulcanizing castable silicone rubber, or polysulfide or epoxy potting material may generally encase the electrical conductors 19 and may generally fill the output end passageway 14 in a sealing relationship with the second wall portion 18. At the input end passageway 15, amoldable plastic electrically insulative member 24,-which-may be such as long glass fiber-filled diallyl phthalate or other suitable filled or unfilled insulating material, such as an epoxy material, generally encases said electrical conductors 19 and may be bounded in a first portion of said input end passageway by the passageway bore wall 22, the end of the input end passageway 15, and by a first wall portion 25 of appropriate material. First wall portion 25 has been made of dielectric material such as borosilicate glass. The distance between any conductor 19 and any other conductive surface or wall should be greater than the wall thickness of sleeve 20. This insures that breakdown occurs across surface 21 and not across surface 42 although nothing said here is intended to restrict the use of this invention to embodiments having sleeve means 20 only on one wall since side wall 25 could just as well be used, either alone or in conjunction with the sleeve 20 of second wall portion 18, as an arc-over surface. The discharge chamber 27 housed by housing 11 and first and second wall portions 25, 18 has the electrical conductors 19 passing therethrough, and may be formed as an extension of bored end as an expansion of bore wall 22 with a supporting shoulder 38 and receiving location for first wall portion 25. The electrical connector housing 1 1 may include venting means or ports 31 communicating between the exterior of housing 11 and discharge chamber 27 to relieve gas pressure of gases (not shown) created during operation of the electrical connector 10. Housing 11 may also be made without ports or vents, or may have the vents permanently plugged, if it is determined that the amount of heat and pressure buildup will not cause such a pressure differential such as to be detrimental to or disruptive of operation of the connector. These venting means 31 may otherwise be normally closed with suitable' sealing means such as frictionally retained caps, hinged, or otherwise attached dust seals 32 to prevent atmospheric contamination or corrosion of the chamber surfaces, but the seal means need not provide a permanent or hermetic seal. Means 31 may also be used to purge the chamber 27 with an appropriate gas in order to reduce the breakdown voltage and/or to reduce the pressure so as to again result in a reduced breakdown voltage. Further, presence of ports or vents 31 assists in cleaning the discharge chamber during manufacturing of these connectors.

In operation, breakdown may initiate by means of an arc at the surface 21 of the electrically insulating sleeve means 20, the are going from conductor 19 to electrically conductive surface 34 of wall 18, and usually forming at a potential lower than the value for air breakdown and thus providing a further advantage over prior art devices that depended only on air or an inert gas breakdown. In addition, a dielectric stimulated arc breakdown may have enhanced impulse ratios (response to fast transients) as will be discussed later.

Sleeve 20 may be of any suitable insulative material but sleeves having good discharge breakdown characteristics as described below may typically be of alumina, rutile, barium titanate and the like. -Materials with high dielectric constants such as greater than about 4 and preferably greater than about 50 tend to show lower static-breakdown voltages and lower impulse ratios and are more suitable for this type of arcover stimulation service. Thus alumina (A1 0 with a dielectric constant of about 8 readily fits into this type of application since itis easily machined and its temperature coefficient of expansion is compatible with widely used conductor materials. Rutile (TiO which has a dielectric constant varying between about 50 and about 100 with a typical value of about 80 is also more brittle but has been found satisfactory in stimulating an arc and thus reducing the threshold voltage. Barium titanate (BaTiO although found to be a good DSA dielectric since it has a dielectric constant varyingbetween about 1000 and about 5000 with a typical value of about 4000 is a more difficult material structurally.

The efficiency of a dielectric to initiate arc-over is seen when comparing voltage requirements for air ver sus a rutile sleeve which may have mil inside diameter and 10 mil wall thickness. In order for an arc to bridge the same air gap, 1.4 kilovolts (kV) are required. The presence of a rutile dielectric will reduce the voltage further to about 1 kV.

In order to provide protection against current or voltage surges in applications such as above, the transient characteristics of the excursions and the resulting discharge should be determined. Given a par static conditions is called the impulse ratio. lmpulse ratio values in air using ramp input waveforms generally range from about 2 to about 6, using alumina as a. dielectric fromabout 1 to about 1.8, and using rutile from about 0.9 to'about 1.2. The general trend of the impulse ratio data is shown in FIG. 4, plotted for linear ramp input waveform with varying rise times for a mil dielectric stimulated arc gap.

.The surface configuration and condition of second wall portion l 8,'conductors 19, and electrically insulating sleeve means 20 at the junction points may affect arc-over characteristics. Good results may be obtained byhaving the electrically conductive surface 34 flush with the sleeve portion end surface 21. The effect of the sleeve end 21 not projecting toa point flush or even with surface 34 results in an increase in the breakdown voltage although, depending upon the use of the connector, the increase may still be within operable limits. This effect does not affect the breakdown voltage to a significant degree unless the difference, in projection'is substantial. When the angle of contact between end 21 and conductor 19 is slightly off perpendicular, the lowest breakdown voltages-occur, other factors being constant. However, this optimum angle is polarity sensitive and, since electrical'current surges from lightning strikes have dual polarity, two optimum angles are formed, dependingupon polarity of surge. Thev breakdown voltages for a perpendicular angle of contact, plus or minus about are not far from minimum and the use of this angle does away with polarity sensitivity as wellias provide-an angle close to optimum. The use of this perpendicular angle of contact, plus or minus about. 15,facilitates manufacture of theseconnectors. Failureto maintain the tolerancefrom, perpendicular does result in a slight increase of breakdownvoltage but generally will allow the connectors: to remain operable. Q f

Surface 39 of sleeve 20- may extend a suitable distance beyond the wall. portion 18. into potting 'material30. This increased distance makes itmore difficult for arc-over to occur atsurfacefl39 versus surface. 21 as well as prevents movement of the sleeve 20 from. thelocation in which it was set. Connectors of this invention wherein surfac e 39 was fromfabout 0.05 inches to about 0.1 inchesfrom support wall 18 have been successful. Electrically insulating sleeve 20 wall thickness may vary depending upon the breakdown voltage desired, type of conductor, current expected, etc.', but may normally be betweenQOOS about 0.030inches.

The ratio of distance, between conductors'19 or 6 irregularities may enhance the arc-over process because of increased field intensification. Surface 21 roughness is preferably kept below about 1 mil rms.

insulating sleeve means 20 and preferably should be about equal. Conductors 19 may have means for interconnecting with appropriate electrical leads and may be cables, wires, pins, etc. Further, these need not be only as long as the housing but could be an electrical conductor line passingthrough body 35 and interconnecting equipment outside of and inside of body 35.

The housing 11 may also'be made of any suitable material, conductive or nonconductive, depending upon economic and safety factors considered. Some suitable conductive materials are stainless steel, aluminurn, copper, nickel, and alloys thereof such as 80% Ni 20% Co alloy. Housings made from 321 and 347 series stainless steels and having wall portion 18 made of 303 and 304 series stainless steels have been successfully used. The housing 11 may be made in segments such as to facilitate manufacturing and assembly processes as long as means providing current conduction from thev second wall portion 18 to the exterior body 35 are provided.' FlG.'5 is a cross-sectional, fragmentary view of one embodiment of this invention wherein the housing 40, 41 is made up of a suitable material which may be plastic or. otherwise nonmetallic. Means 36 are provided for conducting overload currents to exterior body 35. As shown in FIGS. 3 and 5, the second wall portions 18 and 37 respectively, may beeither integral with the housing or aseparate component: with threaded, or the like, means to position and retain the supportwall within the housing.

" First wall portion 25 may be a low dielectric constant insulative member of any suitable material, such as portion 25 is not as significant here, as explained between a conductor 19 and wall za amss surface 42 of electrically insulative first wall'portion 25 to the wall thickness of sleeve 20 should be generally greater than one. This will vary depending upon the. type of rriat ri- I als used ,but maintenance-'about-this value will effectively prevent arc-over across surface 42. A small gap between the sleeve 20. andthe second wall portion 18 or between the sleeve 20-and the conductor or pin 19 above', 'as the ratio of the distance between conductive surfaces" '(such' as conductors l9, and conductive surface 26)"t6 the wall thickness of sleeve 20, which ratio should be generally greater than onenln general, the

material of-wall portion 25 may have a lower dielectric constant than the dielectric sleeve means 20.. Suitable material for first wall portion 25, such as borosilicate glass, are well known and used in the art. In addition, any polysulfide, silicone rubber, epoxy or the like potting material may be used for member 30 as long as a general seal is maintained in the environment in which this connector is to be used.

The electrical connector of this invention may be used at ambient pressure with air or a suitable gas such as neon, hydrogen, argon and mixtures thereof, or at reduced pressure with air and/or a gas from the group listed. Using a 1 mm gap, at pressures less than 5 mm mercury, breakdown voltage is high because of a scarcity of neutral molecules. As the pressure increases, breakdown voltage decreases towards a minimum. Thus, in an air environment with a 1 mm gap, breakdown voltage is minimized at from about 3 to about 7 mm mercury; in hydrogen, at from about 10 to about mm mercury; neon at from about 20 to about 50 mm mercury; and for argon at from about 5 to about 20 mm mercury.

A desirable embodiment of this invention for some instances, as shown in FIG. 3, may use an aluminum alloy body such as A1 60661-T6 series material which has the second wall portion18 and flange means 29 as integral parts thereof. Here the body is machined to the desired shape and anodized so that the resulting anodic coating 33 constitutes the sleeve means equivalentto sleeve means 20 of FIG. 1. This embodiment may eliminate what may be a tedious and generally more expensive need for making dielectric sleeves to a certain dimension to fit over the conductors and within the apertures of the support wall. Conductivity is maintained by grinding or removing the anodic coating off the support wall surface 28 and, secondly, by removing the coating ofi a suitable electrical connector location where contact is made with the body being protected such as the exterior side of the housing in the area of the mounting flange 29. This grinding can be eliminated by the use of appropriate techniques such as masking prior to anodizing.

Although these devices may fail under high-current lightning strikes, fail-safe protection can be facilitated by fusing connector pins. This means that for severe lightning strikes, the-affected connector pins may explode causing molten metal to be deposited around the air chamber, reducing the pin-to-shell breakdown voltage or shorting pins to the metal shell. The explosive nature of the pin failure seems to reliably give the desired deposition of metal around the air chamber.

. The ease with which this can occur relative to the difficulty of eating completely through the metal housing provides a large measure of fail-safe confidence for this invention.

Techniques within the skill of the art to prevent electrical leakage at places other than where arc-over is to occur, may be used. Such techniques are well known in the art and include the use of appropriate adhesives at junctures of dissimilar materials.

What is claimed is:

1. An electrical connector for diverting electrical surges comprising an electrically conductive generally tubular housing, a first apertured wall portion extending transversely of said housing, a second apertured wall portion extending transversely of said housing at a location spaced from said first wall portionforming with'said first wall portion an intermediate discharge chamber and said second wall portion having an exposed electrically conductive surface disposed toward said discharge chamber and electrically communicatconductive areas adjacent said electrically conductive surface, electrically insulating sleeve means encircling said conductors and maintaining them spaced from said second wall portion and from said electrically conductive surface and having sleeve portion ends terminating at locations substantially devoid of projection beyond said electrically conductive surface into said discharge chamber, whereby electrical surges divert from said conductors across said sleeve portion ends to said electrically conductive surface within said discharge chamber and thence to said housing.

2. The electrical connector of claim 1 wherein said generally tubular housing is provided with a plurality of ports therethrough at circumferentially spaced locations and communicating with said intermediate discharge chamber.

3. The electrical connector of claim 2 wherein sealing means is provided over said ports for venting said discharge chamber.

4. Theelectrical connector of claim 1 wherein said tubular housing and said second wall portion are a unitary conductive metal structure.

5. The electrical connector of claim 1 wherein said electrically insulating sleeve means has a dielectric constant, measured at frequencies below about 10 cycles per second at room temperature of about 25 C, of greater than about 4 and wherein said sleeve means is taken from the group consisting of alumina, rutile, barium titanate and combinations thereof which have a substantially constant dielectric constant at frequencies below about 10 cycles per second at about 25 C.

6. The electrical connector of claim 1 wherein the electrical conductors are of about 50 to 54 percent nickel and about 50 to 46 percent ion, and wherein said electrical conductors have coefficients of thermal expansion within about 30 percent of the coefficient of thermal expansion of said electrically insulating sleeve means.

7. The electrical connector of claim 1 wherein said sleeve portions ends are substantially flush with said electrically conductive surface.

8. The electrical connector of claim 1, including gas taken from the group consisting of neon, hydrogen, argon and mixtures thereof disposed in said discharge chamber.

9. The electrical connector of claim 8 wherein said discharge chamber is at a pressure of from about 10 mm to about 20 mm of mercury.

10. The electrical connector of claim 1 wherein said discharge chamber is at a pressure of from about 3 mm to about 7 mm of mercury.

11. The electrical connector of claim 1 wherein the sleeve means has a wall thickness of from about 0.005 inches to about 0.030 inches. 

1. An electrical connector for diverting electrical surges comprising an electrically conductive generally tubular housing, a first apertured wall portion extending transversely of said housing, a second apertured wall portion extending transversely of said housing at a location spaced from said first wall portion forming with said first wall portion an intermediate discharge chamber and said second wall portion having an exposed electrically conductive surface disposed toward said discharge chamber and electrically communicating with said electrically conductive housing, electrical conductors extending through said apertures and said discharge chamber each having exposed electrically conductive areas adjacent said electrically conductive surface, electrically insulating sleeve means encircling said conductors and maintaining them spaced from said second wall portion and from said electrically conductive surface and having sleeve portion ends terminating at locations substantially devoid of projection beyond said electrically conductive surface into said discharge chamber, whereby electrical surges divert from said conductors across said sleeve portion ends to said electrically conductive surface within said discharge chamber and thence to said housing.
 2. The electrical connector of claim 1 wherein said generally tubular housing is provided with a plurality of ports therethrough at circumferentially spaced locations and communicating with said intermediate discharge chamber.
 3. The electrical connector of claim 2 wherein sealing means is provided over said ports for venting said discharge chamber.
 4. The electrical connector of claim 1 wherein said tubular housing and said second wall portion are a unitary conductive metal structure.
 5. The electrical connector of claim 1 wherein said electrically insulating sleeve means has a dielectric constant, measured at frequencies below about 108 cycles per second at room temperature of about 25* C, of greater than about 4 and wherein said sleeve means is taken from the group consisting of alumina, rutile, barium titanate and combinations thereof which have a substantially constant dielectric constant at frequencies below about 108 cycles per second at about 25* C.
 6. The electrical connector of claim 1 wherein the electrical conductors are of about 50 to 54 percent nickel and about 50 to 46 percent ion, and wherein said electrical conductors have coefficients of thermal expansion within about 30 percent of the coefficient of thermal expansion of said electrically insulating sleeve means.
 7. The electrical connector of claim 1 wherein said sleeve portions ends are substantially flush with said electrically conductive surface.
 8. The electrical connector of claim 1, including gas taken from the group consisting of neon, hydrogen, argon and mixtures thereof disposed in said discharge chamber.
 9. The electrical connector of claim 8 wherein said discharge chamber is at a pressure of from about 10 mm to about 20 mm of mercury.
 10. The electrical connector of claim 1 wherein said discharge chamber is at a pressure of from about 3 mm to about 7 mm of mercury.
 11. The electrical connector of claim 1 wherein the sleeve means has a wall thickness of from about 0.005 inches to about 0.030 inches. 